1. Field of the Invention
The present invention relates to optical information readout apparatus and, more particularly, to an optical information readout apparatus, including a readout device having an image forming optical section and a photodetector to be operative to optically readout an information code recorded on a readout object, and a focus shift device for changing a focal position of the image forming optical section.
2. Description of the Related Art
Attempts have heretofore been made in the related art to provide a hand-held optical information readout apparatus for reading out optical information such as a bar code and a two-dimensional code. The optical information readout apparatus is comprised of a body case, formed in for instance a hand-held structure, and a readout device including a photodetector, an image forming optical section having focusing lenses, and an illumination unit or the like that are mounted inside the body case. The illumination device is configured to irradiate an illumination light from a readout opening, formed at a distal end of the body case, onto a readout object (such as a product label recorded with for instance a bar code) to cause a reflection light to be incident on the photodetector to image.
Under such circumstances, a readout distance (a distance between the readout opening and the readout object) for optical information is preliminarily fixed depending on an optical characteristic (of mainly a focus distance) of the image forming optical section assembled to the readout device and a user performs readout operation upon locating the readout device (readout opening) over the readout object by a given readout distance (within a range of a certain degree). In contrast to such an operation, another attempt has been made in recent years to provide a readout device with a mechanism adapted to vary a focal position of an imaging optical section, with the resultant consideration in widening a range of a readout enabling distance available for the single readout device for thereby achieving user-friendliness.
To give an actual example, a readout structure has been proposed which includes an objective taking lens and a CCD detector element between which a focusing disk is provided. The focusing disk, having an outer periphery carrying a plurality (twelve pieces) of optical elements (shims), is caused to rotate for selecting one of the optical elements to change focusing lengths as disclosed in U.S. Pat. No. 6,066,857.
However, with the structure of the optical information readout apparatus incorporating the related art focus shift device using the focusing disk, a need arises for preparing a plurality of optical elements different in thickness, resulting in issues with an increase in the number of component parts and an increase in an overall structure. Further, when changing the focal position, the optical elements (shims) need to be sequentially selected, resulting in deterioration in response time of the readout device. In addition, with the optical information readout apparatus of such a type, no need arises for changing the focusing zones to so many focusing stages resulting in overquality, while causing additional issues with requirements for high precision in positioning the focusing disk.
In the meanwhile, attempts have been made to provide a digital camera and a video camera that incorporate therein zoom lenses or variable focusing lenses for changing best focus positions. However, the variable focusing lenses of such kinds take the form of structures that have increased lens apertures to assure a light intensity and linearly shift best focuses. When applying such structures to the optical information readout apparatus, it takes an extended time period for moving the lenses to a targeted focal position and reading out optical information on the readout object, resulting in remarkable drop in readout speed.